A crawler type Vehicle is disclosed in Japanese Published Unexamined Patent Application No. 59-501501. This vehicle is equipped with a planetary steering differential device and uses a single steering lever device to control rightward/leftward and forward/backward steering of the vehicle.
The known single steering lever device comprises a grip and an upright pivotal movement supporting portion. The grip is grasped by the operator's palm and tilted upwardly, and has a device for transmitting torsional rotary motion. The upright pivotal movement supporting portion has a device for transmitting pivotal movement, which supports the grip so that it can rock on a fixed upright axis within a lateral plane. The former torsional rotary motion transmitting device is coupled through a mechanical link to a forward/backward change valve of a speed change gear so that the crawler type vehicle is driven forwardly or backwardly or is in neutral. The latter pivotal movement transmitting device is coupled through the mechanical link to a change valve. The change valve changes the direction in which a steering hydraulic motor rotates. The steering hydraulic motor inputs rotary power of differential steering to the planetary steering differential device. The crawler type vehicle can be driven straight or pivoted rightwardly/leftwardly.
Steering the vehicle using the former device is easy since the desired movement of the vehicle is obtained by rotating the operator's wrist in the direction in which the vehicle is to move, that is, when the grip is moved forwardly while the grip is being rotated, the vehicle moves forwardly, whereas when the grip is moved backwardly while the grip is being rotated, the vehicle moves backwardly. However, pivoting the vehicle using the latter device has a disadvantage.
That is, even when the grip is rocked backwardly and then is rocked rightwardly or leftwardly for pivoting the vehicle, the rocking direction does not agree with the pivoting direction. The problem of the conventional art is that the vehicle does not pivot in the direction in which the lever is rocked.